The invention relates to a display device, in particular for a motor vehicle, having a pointer, a scale and an electrooptic display, it being possible to represent measured values on the scale in an analog fashion using the pointer, and at least one area of the electrooptic display being arranged along the movement path of the pointer.
Such display devices are known and are principally used in motor vehicles to display a travel speed or an engine speed. The electrooptic display has in such cases display segments with a defined, nonvariable shape. It is therefore not possible to represent any kind of information or graphics as desired.
Other known display devices having an analog pointer-type round instrument and a display over which said pointer passes in order to represent variable information have a large scale face which can be actuated, it being possible to actuate in a variable fashion all the display elements including the scale divisions and to represent them on the display. The size of the display face which can be actuated is a direct measurement of the fabrication costs of the display and thus of the display instrument, as a result of which these known display instruments are very expensive. Furthermore, the representation on the display is limited to a display mode which is made up of individual, approximately quadratic picture elements, as a result of which arcuate elements can only be represented in an approximated way and with incremental jumps which make the display more difficult to read. This is particularly disadvantageous in the case of display elements which are assigned to the (round) scale.
The invention is therefore based on the object of designing a display device of the aforementioned type in such a way that it provides an analog representation of measured values using a pointer instrument and an unlimited way of presenting information including displays on the electrooptic display which correspond to the scale, while at the same time the fabrication costs for the display device are low.
This object is achieved according to the invention in that the electrooptic display has a first display field which runs along at least one section of the movement path of the pointer and has display segments which can be actuated, and a second display field which can be actuated in an unrestricted way.
Thus, different types of representations can easily appear independently of one another on the two display fields. For example, the first display field can have defined display segments which are adapted to the geometry of the scale and of the movement path of the pointer. The first display field ensures that the measured values which are represented on the scale using the pointer, and further information which is visualized by actuating the display segments, can be read easily and reliably. The number of display segments of this display field may be comparatively low here, because only a limited number of geometries have to be represented. The adaptation of the display segments to the necessary geometries avoids undesired step increments in the representation. On the other hand, the second display field, which can be actuated in an unrestricted way, serves for the unrestricted representation of information. Here, for example graphics, such as route indications of an application system, video sequences or, in certain cases, warning signals, can be displayed. In this way, the display device according to the invention combines the possibility of representing various types of information in an unrestricted way with an instrument which can be read easily and reliably. This implements a high level of information density with, at the same time, a display which is easy to read.
It would be conceivable to use a cathode ray tube or a vacuum fluorescent display for the electrooptic display. However, the display device can be fabricated particularly cost-effectively and in large numbers if the electrooptic display advantageously has a liquid crystal display. In particular, when used in motor vehicles, the liquid crystal display provides further advantages, because it has only a low electric power drain and, by virtue of its flat design, requires only a small installation space.
The electrooptic display can be fabricated cost-effectively and easily if, in accordance with another advantageous development of the invention, the liquid crystal display is a TN or STN display. Such displays are additionally very operationally reliable and, in particular, STN displays are easy to read even with extreme viewing angles.
According to another advantageous development of the invention, the display has the first display field with display segments which can be actuated, and the second display field, which can be actuated in an unrestricted way, in the same display plane, with the result that, on the one hand, the number of production processes necessary to fabricate the display is low and, on the other hand, it is ensured that the two display fields can be read simultaneously in an easy, precise way, free from parallax.
The actuation of the electrooptic display can advantageously been simplified if it has two liquid crystal displays which are arranged optically in series. The first display field with segments which can be actuated is preferably arranged on a first of the liquid displays and the second display field, which can be actuated in an unrestricted way, is arranged on the second liquid crystal display. In this way, the displays can be designed in a way which has optimum adaptation to the different requirements, it being also possible largely to prevent them influencing one another electrically. In this way it is also easily possible to provide, for example, a display with a first display field which is adapted to a defined scale and has display segments which can be actuated, and to select the liquid crystal display which is arranged optically in series with said display and which has the second display field which can be actuated in an unrestricted way, either as a monochrome display or color display depending on the individual wishes and requirements.
A way of representing information in a particularly unrestricted way over a large area (for example to show a video film) which is particularly attractive if there is no representation on the first display field (for example when the vehicle is stationary), can preferably be obtained if the display fields overlap at least partially.
The necessary installation space for an electrooptic display which has two liquid crystal displays which are arranged optically in series is, according to another advantageous development of the invention, particularly small if the electrooptic display has a DSTN display.
A maximum, physical integration of the elements of the display can be achieved if the electrooptic display advantageously has a multilayer liquid crystal display having on a substrate at least two electrode layers, which are electrically separated from one another and can be actuated independently. Although it continues to be possible to represent a plurality of display fields with such a design, all that this requires is a single liquid crystal cell with one front wall and one rear wall, each fitted with electrodes, a liquid crystal substance being enclosed between the walls. In this context it is particularly favorable, and simplifies the design, if the first display field with display segments which can be actuated can be represented with a first of the electrode layers and the second display field, which can be actuated in an unrestricted way can be represented with the second electrode layer.
A particularly wide variety of information can be represented in an unrestricted way with the display device if the second display field, which can be actuated in an unrestricted way is preferably a dot matrix field which can be actuated using a multiplex method. Despite the possibility of actuating a large number of picture elements, the multiplex method requires only a comparatively low amount of structural work for the display device.
According to another advantageous development of the invention, the second display field, which can be actuated in an unrestricted way, can be actuated using an anti-aliasing method. This provides image smoothing which, in particular also when representing moving imagesxe2x80x94leads to a clear display and thus one which can be read and recognized better.
It is possible to conceive of representing dark characters on a light background on the electrooptic display, but this makes the display more difficult to read, in particular when there is low ambient light the large background surface can have a dazzling effect on a viewer. Since motor vehicles with display instruments which cannot be read so well also have the direct effect of also reducing traffic safety, such disadvantages must be avoided. It is therefore particularly advantageous if light characters can be represented on a dark display area using the electrooptic display.
A particularly good contrast between the characters represented and the rest of the display area forming the background of the display, and between said characters and the nonselected characters is advantageously achieved if nonselected display elements can be actuated with an actuation voltage (undershoot range) which has a minimum transmission. In this context, use is made of the effect experienced in liquid crystal cells, according to which an actuation voltage lying between an actuation voltage which gives rise to a high level of transmission and a nonactuation voltage which gives rise to a low level of transmission leads to a minimum level of transmission of the liquid crystal cell.
The pointer of the display device may, for example, execute a linear movement along a linear scale in order to display measured values. However, such a display device is difficult to read because the entire display region is difficult to perceive with one glance. Rapid assessment, necessary in particular in motor vehicles, of the relative magnitude of the displayed measured value is therefore only possible with difficulty. It is therefore of particular advantage if, according to another advantageous development of the invention, the movement path of the pointer describes a circular arc segment, and the entire display region of the pointer, together with the position of the pointer, can be perceived in a very short time.
According to another advantageous development of the invention, a travel speed can be displayed with the pointer, and a set value of a speed regulating system can be represented by actuating at least one display segment of the first display field. In this way, a mark or a band of display segments directly in the vicinity of the scale and of the movement path of the pointer can be used to represent the preset speed. Furthermore, important operational data of the vehicle such as fault messages or navigation instructions can be displayed on the second display field which can be actuated in an unrestricted way. In this way, the display device according to the invention provides a comprehensive way of representing information which can be read and absorbed easily by a vehicle driver, the possibility of him being distracted from the traffic situation being thus reduced to a minimum, unavoidable level.